Absolutely acknowledge it 😉
Seriously though, definitely bring it up when asked about research experience in the primary/secondaries and definitely the research as an activity and mention your contribution to the paper. IF they specifically ask for publications, don't list it as one but enter it as an acknowledgment. Also, if those are some really neat figures with meaning behind them, keep copies and maybe you can show them off at interviews if asked about the research you've done.
I really think this whole deal with undergraduates expecting publications is strange and just reflects the negative effects of overcompetitiveness. Most of my classmates tell me that on their publications, all they were doing was following protocols and were rewarded for their hard work with a authorship. In medical school, patient chart reviews serve as the predominant form of authorship in my experience and even those aren't too involved. OP, you're ahead of the gaming for what you have. Just list it as it is, and I think it will be viewed favorably. If you're going into the cycle with a top 20 or bust mentality, maybe that's a different story. That being said, one of my good friends currently at a top research school for his MSTP never actually got an authorship out of his main project. It was probably frustrating for him seeing as how he worked so hard, but he still was able to write an exceptional MD/PhD essay. You;ll have a siilar experience if you choose to make this one of your 3 major experiences.